In general, protein kinases are the largest set of structurally related phosphoryl transferases, have highly conserved structures and catalytic functions and may be categorized into families by the substrates they phosphorylate (e.g., protein-tyrosine, protein-serine/threonine, histidine and the like) and are responsible for the control of a wide variety of cellular signal transduction processes.
Examples of protein-tyrosine kinases include, but are not limited to, Irk, IGFR-1, Zap-70, Bmx, Btk, CHK (Csk homologous kinase), CSK (C-terminal Src Kinase), Itk-1, Src (c-Src, Lyn, Fyn, Lck, Syk, Hck, Yes, Blk, Fgr and Frk), Tec, Txk/Rlk, Abl, EGFR (EGFR-1/ErbB-1, ErbB-2/NEU/HER-2, ErbB-3 and ErbB-4), FAK, FGF1R (also FGFR1 or FGR-1), FGF2R (also FGR-2), MET (also Met1 or c-MET), PDGFR-α, PDGFR-β, Tie-1, Tie-2 (also Tek-1 or Tek), VEGFRI (also FLT-1), VEGFR2 (also KDR), FLT-3, FLT-4, c-KIT, JAKI, JAK2, JAK3, TYK2, LOK, RET, TRKA, PYK2, ALK (Anaplastic Lymphoma Kinase), EPHA (1-8), EPHB (1-6), RON, Fes, Fer or EPHB4 (also EPHB4-1).
Examples of protein-serine/threonine kinases include, but are not limited to, Ark, ATM (1-3), CamK (I-IV), CamKK, Chk1 and 2 (Checkpoint kinases), CKI, CK2, Erk, IKK-I (also IKK-ALPHA or CHUK), IKK-2 (also IKK-BETA), Ilk, Jnk (1-3), LimK (1 and 2), MLK3Raf (A, B, and C), CDK (1-10), PKC (including all PKC subtypes), Plk (1-3), NIK, Pak (1-3), PDK1, PKR, RhoK, RIP, RIP-2, GSK3 (A and B), PKA, P38, Erk (1-3), PKB (including all PKB subtypes) (also AKT-1, AKT-2, AKT-3 or AKT3-1), IRAK1, FRK, SGK, TAK1 or Tp1-2 (also COT).
Protein kinases play very important roles in the normal regulation of cell growth. However, as a result of either mutation or overexpression of the tyrosine kinases (receptor or non-receptor) or the ligands of the receptor tyrosine kinases, signaling can become deregulated, resulting in uncontrolled cell proliferation leading to cancer or a related disease.
Protein kinases catalyze and regulate the process of phosphorylation, whereby the kinases covalently attach phosphate groups to proteins or lipid targets in response to a variety of extracellular signals: hormones, neurotransmitters, growth and differentiation factors, cell cycle events, environmental stresses, nutritional stresses and the like.
Phosphorylation modulates or regulates a variety of cellular processes such as proliferation, growth, differentiation, metabolism, apoptosis, motility, transcription, translation and other signaling processes. Uncontrolled signaling for cell growth due to defective control of protein phosphorylation has also been implicated in a number of diseases, such as osteoarthritis, rheumatoid arthritis, synovial pannus invasion in arthritis, multiple sclerosis, myasthenia gravis, diabetes mellitus, diabetic angiopathies or retinopathy, inflammatory bowel disease, Crohn's disease, ulcerative colitis, transplant or bone marrow transplant rejection, lupus, chronic pancreatitis, cachexia, septic shock, skin diseases or disorders (such as papilloma formation, psoriasis, dermatitis, eczema, seborrhea and the like), central nervous system diseases (such as Alzheimer's disease, Parkinson's disease, depression and the like), cancers (such as glioma cancers, epidermoid cancers, head and neck cancers, lung cancers, breast cancers, colorectal cancers, prostate cancers, gastric cancers, esophageal cancers or papillocarcinomas and the like and associated pathologies such as unregulated cell proliferation, tumor growth or vascularization or metastatic cancer cell invasion and migration and the like or leukemias or lymphomas), occular diseases (such as macular degeneration, diseases of the cornea, glaucoma and the like), viral infections (such as cytomegalovirus CMV), heart disease (such as atherosclerosis, neointima formation or transplantation-induced vasculopathies (such as restenosis and the like)) lung or pulmonary diseases (such as allergic-asthma, lung fibrosis or complications resulting from chronic obstructive pulmonary disorder and the like) or kidney or renal diseases (such as acute, subacute or chronic forms of glomerulonephritis or membranoproliferative glomerulonephritis, glomerulosclerosis, congenital multicystic renal dysplasia, kidney fibrosis and the like). Therefore, kinase inhibitors have potential use as therapeutic agents.
The tyrosine kinases can further be categorized by whether they are receptor tyrosine kinases or non-receptor tyrosine kinases. The receptor tyrosine kinases span the cell membrane with a ligand interacting domain protruding from the cell, with a hydrophobic trans-membrane domain, and a cytoplasmic domain that contains the catalytic kinase domain and other regulatory sequences. Non-receptor tyrosine kinases are often myristylated or modified by the addition of other hydrophobic moieties that allow them to be anchored to the cell membrane.
The epidermal growth factor receptor (EGFR) tyrosine-kinase family includes the receptors EGFR (also referred to as EGFR-1 or Erb-B1), HER-2 (or neu), EGFR3 and EGFR4. Epidermal Growth Factor (EGF), Transforming Growth Factor-α (TGF-α) and the HER-3 ligand heregulin are three of the ligands that bind to the EGFR receptors.
For example, EGFR overexpression or mutation of one or more EGFR kinase family members has been commonly involved in cancer and other diseases characterized by uncontrolled or abnormal cell growth. Deregulation of EGFR has also been associated with epidermoid tumors, head and neck tumors, breast tumors and tumors involving other major organs. Diseases associated with increased EGFR expression include proliferative glomerulonephritis, diabetes-induced renal disease and chronic pancreatitis. Overexpression of HER2 has been associated with breast and ovarian cancer. Diseases associated with the overproduction of TGF-α, rather than overexpression of EGFR, include psoriasis, a cell-proliferative skin disorder. Since EGFR expression levels in uterine tissues are elevated during implantation of a fertilized egg, an EGFR inhibitor may also have potential use as a contraceptive to reduce fertility.
Human cytomegalovirus (CMV) is a widespread opportunistic human herpes virus that causes severe and fatal diseases in those who are immune compromised and in transplant recipients. CMV is also a leading cause of atherosclerosis and virally mediated birth defects. The human CMV uses the EGFR receptor to enter cells during infection, EGFR is autophosphorylated and the downstream signal transduction pathway components are activated; however, the EGFR specific inhibitor tyrphostin AG 1478 has been shown to reduce the viral load in cells that were infected in the presence of the tyrphostin (Wang, et al., Nature, 24 Jul. 2003, Vol 424). Accordingly, potent EGFR selective inhibitors may be useful in anti-CMV therapy.
The Src family of tyrosine-kinases includes the sub-family proteins c-Src, Lyn, Fyn, Lck, Syk, Hck, Yes, Blk, Fgr and Frk. While various members of the c-Src family are important for normal cellular proliferation, their overexpression and overactivation can promote development of cancer (Yeatman T J, Nature, June 2004, Vol. 4). For example, the Lyn kinase has been shown to be upregulated in hormone resistant prostate cancer. Tumor xenografts of hormone resistant prostate cancer cells showed delayed growth upon treatment with peptides that specifically block Lyn kinase activity (Goldenberg-Furmanov, et al., Cancer Research, 1 Feb. 2004, 64, 1058-1064).
The Lyn and Hck Src sub-family tyrosine-kinases have both been implicated in chronic myeloid leukemia (CML). CML is caused by the BCR-Abl fusion protein that results from the t(9;22) chromosomal translocation that juxtaposes the c-Abl non-receptor tyrosine kinase gene on chromosome 9 with a breakpoint cluster region (bcr) gene on chromosome 22. The BCR-Abl fusion protein is a constitutively activated form of the Abl tyrosine kinase that drives uncontrolled growth leading to CML and many cases of adult acute lymphoblastic leukemia. Gleevec, which is an inhibitor of Abl has been successfully used to treat CML. However, Gleevec does not help patients in blast crisis because they carry mutant forms of BCR-Abl that no longer bind Gleevec. Such Gleevec resistant CML cells are sensitive to a dual src/BCR-Abl inhibitor that binds and inhibits the mutant BCR-Abl and members of the src family (Shah, et al., Science, 16 Jul. 2004, Vol 305, 399-401). There are also other ways that CML cells can become resistant to treatment with the tyrosine kinase Abl inhibitor Gleevec. For example, CML K562 cells that become resistant to Gleevec minimize reliance on the BCR-Abl translocation for growth and instead upregulate the Lyn and Hck kinases. This was demonstrated by expressing antisense Lyn in these cells, which reduced their rate of proliferation (Donato, et al., Blood, 15 Jan. 2003, 101(2)). c-Src and other Src family members are also involved in cellular adhesion, invasion and motility of tumor cells. Thus, small molecule inhibitors of the Src kinase family could offer new therapeutic opportunities for both leukemias and solid tumors.